Hemoccult test was performed on stool specimens of 249 patients; 64 with advanced renal failure prior to dialysis (CRF), 144 on maintenance hemodialysis (HD), and 41 receiving chronic ambulatory peritoneal dialysis CAPD. Each patient collected spontaneously evacuated stool specimens on three different days. None of the patients had overt gastrointestinal bleeding prior to participation in the study. The patients were not taking aspirin, or any other ulcerogenic medication, nor receiving iron supplements at the time of study. Twelve of 64 CRF patients (18.8%), 9 of 144 HD subjects (6.3%), and 3 of 41 CAPD patients (7.3%) had Hemoccult positive stool. Twenty patients underwent diagnostic gastrointestinal (GI) evaluation and these studies demonstrated a definite GI pathology. The commonest lesion was duodenal involvement (alone or in combination with other lesions) and was found in 61.1% of the subjects. The duodenal lesions consisted of superficial erosions, duodenitis, ulcers, polyp, and arteriovenous malformation. The other common lesions were gastritis and hemorrhoids. These results underscore the need for utilization of a simple and non-invasive Hemoccult test in patients with ESRD routinely, and the positive test should be followed by a thorough gastrointestinal work up to identify the cause of occult bleeding.